Leather articles, particularly leather garments, are often cleaned by processes that remove dirt and grease with an aqueous solution of soap, synthetic detergent, ammonia, or some other cleaning agent, or by treating the leather with an organic solvent. None of these techniques is completely satisfactory because each tends to have a deleterious effect on the leather.
Cleaning suede is a more difficult problems than cleaning leather, since suedes do not tolerate water. The commonly used methods for cleaning suede leather involve the use of petroleum-based solvents in a type of dry-cleaning process. Spot removal may be accomplished by the use of a chlorinated hydrocarbon, often applied in the form of a spray.
The problem of cleaning leather, without adversely affecting it, has been recognized for a long time. In U.S. Pat. No. 1,100,436, granted June 16, 1914, soiled gloves were placed in open mesh bags together with small sponges; immersed in a mixture of gasoline, caustic potash or ammonia, and a fatty acid such as oleic acid; and heated and tumbled in an inert atmosphere. The sponges produced a gentle, kneading action that cooperated with the solvent and rinsing action of the gasoline. Needless to say, such treatment would not only remove accumulated grease, dirt, perspiration, and stains, it would destroy the suppleness, resilience and hand of the leather, to say nothing of the fire hazard involved.
Bennett's The Chemical Formulary, Chemical Publishing Co., Vol. 1 (1933), p. 77, describes a leather cleaner made by dissolving soap in water, then adding ammonium hydroxide, glycerine, and ethylene dichloride. There are no directions for use, but clearly, the glycerine was added in the hope of compensating for the harsh action of the other materials. The same volume, on page 431, describes a suede cleaner made from a mixture of chalk, quilaya bark, cream of tartar, and oil birch tar. Once again, there are no directions for use of this suede cleaner preparation, or as a matter of fact, for the method of preparing it.
Later editions of Bennett's Formulary repeated substantially the same leather cleaner recipe that appeared in the 1933 edition above: see for example Vol. 5 (1941), at page 571, and Vol. 7 (1945), pages 373 and 374.
A somewhat different approach is described in U.S. Pat. No. 2,161,504, granted June 6, 1939. The patented invention there is based on the discovery that vulcanized oils are particularly suitable as an abrasive material for cleaning leather skins to produce a buffed surface. The patent points out that vulcanized oils are made by treating vegetable oils with sulfur chloride. For the purposes of the inventon, these vulcanized oils are reduced to particulate form, and then are placed in a drum together with the leather skins that are to be cleaned. The skins or other leather articles are then subjected to tumbling with the particulate vulcanized oil, to produce a mild abrasive action. The particles are then removed from the leather by brushing.
The Davis patent, U.S. Pat. No. 2,766,134, granted Oct. 9, 1956, faced a somewhat different problem. Davis was concerned with restoring the original appearance of leather that had been impregnated with a material such as rubber, oil, wax, of polymerized wood rosin. To effect the restoration, the impregnated leather was washed in a solvent, such as gasoline, for a period of time sufficient to dissolve only the impregnant immediately adjacent the surface of the impregnated leather, then the solvent was removed by washing with a second solvent miscible with the first solvent but inert to the leather, and then the impregnated leather was washed in water. Strictly speaking, this was not a cleaning technique but an attempt to remove an impregnant. Despite the presence of the impregnant, it is doubtful that the water washing step exerted any kind of beneficial effect on the leather.
A higher level of sophistication, in suede treatments, appears in U.S. Pat. No. 2,876,130, granted Mar. 3, 1959, where suede was treated, not to clean it, but to apply an optical brightening agent to brighten the appearance of the suede.
The usual kind of dry cleaning approach, for cleaning leather gloves, was described in the Bulletin Service of the National Institute of Dry Cleaning, May, 1959, pages 38 and 39. This bulletin, intended for professional use only, suggested the use of a mixture of dry cleaning detergent with several parts of dry cleaning solvent. The article pointed out that some detergents, when used in a wet stock solution, will not rinse completely from the leather and will leave a yellow stain. No suggestion was made for avoiding the problem other than checking with the manufacturer of the detergent to see whether any particular detergent would be suitable for use in this manner. Additional details on cleaning suede garments appeared in the same publication in its January, 1962 issue, page 51. This publication points out that the dry cleaning cycle may take anywhere from 15 to 35 minutes, in petroleum equipment, depending upon how dirty the suede garment is. Several extraction, rinse, and extraction steps are suggested, with tumbling being conducted at a temperature not over 140.degree. F., to avoid shrinkage. The publication recognizes the great tendency of water to spot suede, and the possibility of the loss of dye in an area that is being cleaned by the "spotting" technique. The second paragraph in the article points out that the dry cleaner must explain to customers that leathers must not only be dry cleaned but also refinished to restore their original appearance. No comment is made about the need for restoring other qualities of the leather that may have been adversely affected by the dry cleaning operation.
At least as early as 1967, Bennett's Formulary had become more elaborate in its suggestions for leather cleaning compositions. In Vol. 13 (1967), at pages 392 and 393, the Formulary suggests a leather cleaning composition containing silicone oil, oleic acid, mineral spirits, water, and other ingredients that are identified by trademark only. Directions are provided for mixing the ingredients for the leather cleaner, and for using it. The cleaner is to be applied with a clean cloth, followed by buffing.
Although prior art solvent cleaning methods generally are or can be made effective for removing dirt, fading, stiffness and other poor effects, such as a loss of "hand", are usual concomitants of prior art cleaning methods. Moreover, heavily soiled spots present a special problem. They are very difficult or impossible to clean with water-based agents, and the use of organic solvents often leaves a ring much larger in area than the original spot. Suede leather will tolerate dry cleaning agents less well than grain leather, and repeated applications of organic solvents have pronounced negative effects on suede leather. Greasy spots are virtually impossible to clean on suede, especially spots that result from perspiration around the neck and around the cuffs.
Professional dry cleaning techniques offer the only effective approach for cleaning heavily soiled grain leather and suede, and the end results are often not satisfactory because of the undesirable effects of solvents on the materials.